In a muscle fibre, `Ca^(++)` is stored in ...

Explanation

### Step-by-Step Solution:

1. **Understanding Muscle Fiber Structure**: Muscle fibers are specialized cells that contain various organelles, including the endoplasmic reticulum, which plays a crucial role in muscle contraction.

2. **Identifying the Role of Calcium Ions**: Calcium ions (Ca²⁺) are essential for muscle contraction. They facilitate the interaction between the contractile proteins in muscle fibers.

3. **Locating Calcium Storage**: In muscle fibers, the endoplasmic reticulum is specifically referred to as the **sarcoplasmic reticulum**. This structure is responsible for storing calcium ions.

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